The ambiance and physical sensation associated with a natural flame such as those found in campfires and fireplaces are widely desired. But because of a number of economic and environmental issues, including the pollution and physical mess of wood burning, the use of wood-burning appliances and open campfires has been severely restricted in recent years. There have been a number of attempts to produce a realistic appearing system of synthetic logs, burning wood pellets, natural gas, propane, LPG, or butane that would duplicate the ambiance of wood burning without the liabilities. Several systems have reached the market place and have enjoyed some commercial success. However, none of these systems have achieved the appearance, ambiance, and functional realism of real wood fires.
Gas log devices currently are all constructed on a similar pattern. The gas is burned by allowing it to escape from a series of small holes in a metallic tube or more complex burner device. The burner is then positioned under an artificial log in an attempt to simulate a natural log. The resulting gas flame is then allowed to play across a series of artificial log shapes to produce the visual illusion that the logs are actually burning. Prior to the instant invention, in all cases, the degree of realism relies on successfully hiding the obviously artificial nature of the burner itself. This is usually accomplished by placing the burner and its flames below and/or behind one or more of the artificial logs. To enhance realism, the design of the shapes of the artificial logs and the placement of the burner restricts the viewing area of the flames to those areas that look most realistic and to prevent viewing of the burner. Thus, area over which the flame may be viewed is small. A more realistic design is impossible with this technology because much of the flame must be hidden from view to prevent view of the artificial burner from some angles, or view of jets of flame suggesting that gas rather than wood was being burned.
Using current technology, a designer of an artificial log device must somewhat restrict the view of the flames to those portions that appear more natural, such as the upper part of the flame. Similarly, view of the burner must be obstructed by placement of a log or other obstruction in the predicted line of view. Unfortunately, a trade-off results in that to completely obstruct the view of the burner, the view of the logs and flames must be excessively blocked. As a result, in most applications, the burner is sometimes visible and portions of the flame, which are somewhat attractive, are sometimes blocked from view.
The need to block the view of the burner severely restricts the emission of radiant energy, primarily infrared (IR), that can be emitted by the flame. For those designers hoping to capture a portion of the available heat from the device, it is then necessary to place a heat exchanger in the hot zone above the flames, and to provide a blower system to force the resulting heated air into the surroundings.
Using such heat transfer devices allows a person near the prior art artificial logs to feel warmth from a stream of moving hot air. The resulting sensation is unlike a real wood fire, in part because the IR does not warm the person. In fact, the radiant or IR portion of the available energy is simply lost, having been blocked by the artificial logs that prevent view of the burner. These disadvantages seriously degrade the sensory illusion of the fire and combine with visual discrepancies related to the use of burners and the need to block view of the lower portions of the flames.
The artificial logs of the current art are generally formed by one of two candidate technologies. In the older of these, a ceramic or cementitious material is cast into a mold. Sometimes the mold is derived from a natural log. As an alternative, particularly when the xe2x80x9clogxe2x80x9d shape needs to conform to a specialized geometric requirement of the fireplace or gas stove, the mold is created by copying a machined or carved piece of some easily worked material such as plaster, plastic foam or soft wood. This piece is generally a xe2x80x9cpositivexe2x80x9d of the desired final log shape. From the man-made xe2x80x9cpositive,xe2x80x9d a xe2x80x9cnegativexe2x80x9d is generally constructed of some material, which then provides the cavity into which the xe2x80x9clog materialxe2x80x9d will be cast or otherwise placed. The xe2x80x9cnegativexe2x80x9d provides copies (castings) that are as nearly identical as possible to the original positive. These pieces generally are lacking the realism of a natural piece of wood because of the extensive effort needed to actually duplicate the almost infinite complexity of a piece of natural wood, either split or bark covered. Another disadvantage is that the ceramic or cementitious material that is cast into such a mold is generally quite dense, hard, and of necessity must be quite refractory to allow it to withstand the play of flames over it at temperatures often exceeding 1300 F. Given these design and performance constraints, it is not surprising that these high-density logs are not xe2x80x9cactivexe2x80x9d in the sense of contributing more than their physical shape to the creation of the fire illusion. And in fact, they actually act as a large heat sink, absorbing both the visible light and the IR emitted by the flames, significantly reducing the warmth, which would otherwise be radiated. A person sitting by the fire feels very little warmth and sees very little light. In a dimly lit room, the logs are generally only visible as a dark profile, while the flames play around them in a predetermined and usually near-static pattern. This is not a very convincing illusion of a real wood fire, and is not a very efficient or pleasant way to provide heat to the room. For applications involving portable campfires, these logs would be wholly unsuitable because they are very heavy. A set of such logs would generally involve the use of 1-2 gallons of the liquid castable material to provide the necessary log shapes, and therefore would typically weigh approximately 30-40 lbs, not including all the accompanying fittings and other structure. This excessive weight would make design of any portable device difficult or impossible.
A more modern alternative method of creating the artificial logs employs the technology of vacuum-formed ceramic fibers to produce lightweight log shapes. These ceramic fiber logs are xe2x80x9csemi-active,xe2x80x9d emitting a glow in response to the play of the flame and reducing the heat sink effect. They are also significantly lighter, presenting the possibility that they could be used in a portable device. However, they suffer from their own set of limitations. These limitations arise primarily from the limitations of the vacuum-forming technique itself. All such logs will of necessity have at least one side that must remain hidden from the viewer because it has no log-like detail and is essentially a flat surface. This results because at least one side of the vacuum-mold must remain open to the slurry from which the log is made. That surface will be random and slightly lumpy because that is the way that the slurry of fibers naturally flows under the influence of the vacuum. Furthermore, in order to allow the wet fiber shape to be removed from the vacuum mold, the logs generally are restricted to those having more planar surfaces rather than the detailed, curved surfaces of natural bark-covered wood. It is far easier to give the illusion of a planar, split piece of wood than it is to create a vacuum mold that has the fully round natural shape. With considerable creativity and clever placement, the vacuum-formed logs can be made to appear more natural when burning than the heavy ceramic logs, but the illusion is still incomplete, especially so since the vacuum-formed logs have the extra restriction of being unable to achieve a full round shape. And, because the ceramic fiber logs only provide an illusion of being on fire, they still require the use of a hidden metallic tube or similar burner. The viewing area must, in many cases, be even more restricted than with the high-density ceramic logs to hide both the burner and the unnatural and incomplete shape of the logs.
In either of the logs of the current art, providing other components that typically are found in a real wood campfire is difficult or impossible. Adding, for example, a ring of rocks such as many people use around a campfire could not be easily included in with the current art. High density ceramics would simply add far too much weight if used. Vacuum-formed materials are generally so fragile that they would be very easily damaged during normal handling and normal use in a camping environment.
For the foregoing reasons, there is a need for an artificial log that can does not require a burner or similar structure to produce flame, which can be arranged in a natural-looking manner without regard to hiding such a burner, and which allows the emission of a greater quantity of IR energy because the hot lower portions of the flame do not have to be obscured to hide the artificial appearance of the burner. Moreover, there is a need for an artificial log that is cooled by the flow of natural gas or propane flowing through it, and which thereby more effectively discharges heat energy during the combustion process. Such a convection-cooled log would have the further advantage of providing a stable, long lasting environment for the gas tube. Stresses, corrosion, oxidation and disbandment between the tube material and the log material would be minimal.
The present invention is directed to an apparatus that satisfies the above needs. A novel gas burning artificial log and method of manufacturing is disclosed, which does not require a burner or similar structure to produce flame; which can be arranged in a natural-looking manner without regard to hiding such a burner; which allows the emission of a greater quantity of IR energy because the hot lower portions of the flame do not have to be obscured to hide the artificial appearance of the burner; and which is sufficiently porous at the microscopic and semi-microscopic level to allow natural gas or propane flowing through it, resulting in surface flames having a more realistic appearance and also in a cooler log due to convection heat transfer from the log resulting from the gas movement through the log. The pores are sufficiently small as to provide a continuous appearance to the flame.
The gas-burning log of the instant invention is adapted for use with gas-burning fireplaces, portable xe2x80x9ccampfires,xe2x80x9d decorative patio fireplaces and other applications. The gas burning artificial log and method of manufacture of the present invention provides some or all of the following structures and manufacturing steps.
(A) An active log 20 receives a supply of gas from an external supply. A preferred active log is made of a material having sufficient microscopic porosity to allow gas to move through the material from which the log is made, typically moving from an internal location to the surface of the active log. Gas moving through the log absorbs heat energy, thereby cooling the log by convection and warming the gas prior to combustion. Gas, which is smoothly exhausted from pores on the outer surface of the log, is burned, thereby creating a realistic approximation of the appearance of a real log burning.
(B) A process for manufacturing active logs, comprising some or all of the following steps.
(a) Assembling, a liquid part A, in a preferred embodiment comprising: colloidal silica, 55-65% of final mix weight; ceramic bulk fiber, 3-5%; xc2xdxe2x80x3 glass needles, 1-3%; fluorocarbon wetting agent, 0.2-0.3%; and Triton X-100 or similar foaming agent, 0.6-0.8%; wherein the total % of final mix weight is approximately 67%.
(b) Assembling a solid part B, in a preferred embodiment comprising: insulating, lightweight refractory fillers, such as lightweight filler thermal insulation microspheres with thin walls, 15-17% and lightweight filler thermal insulation fly ash ceramic microspheres with thick walls, 2-4%; light weight filler of foamed silica perlite, 3-5%; light weight filler ultra light ceramic microspheres, 3-5%; anhydrous sodium silicate powder, 2-4%; anhydrous potassium silicate powder, 2-4%; wherein the total % of final mix weight is approximately 33%.
(c) Whipping the liquid part A while the solid part B is added, thereby making the mixture homogeneous and lowering the density of the mixture by the addition of air introduced by the whipping action. The introduction of air also results in the formation of microscopic pores and interconnected air pockets through the material. The whipping action is typically contained until the weight of the mixture is approximately 3.8 to 4.5 pounds per gallon.
(d) Placing the whipped mixture into a mold carrying a gas tube 40, curing the mixture and demolding.
(C) Whereby the gas tube 40, encased within the active log during the molding process, defines holes through which natural gas or similar fuel may be exhausted.
(D) A gas supply line 60, attached to the gas tube 40, provides a continuing supply of gas fuel.
(E) One or more passive logs 80, manufactured in a manner similar to that of the active logs, but having no gas tube 40, may be carried adjacent to the active logs in some applications.
It is therefore a primary advantage of the present invention to provide a novel gas burning artificial log and a method or manufacturing such logs from sol-gel compositions wherein the burner used behind or under conventional artificial logs is replaced by an active log having sufficient porosity to allow gas exhausted from a pipe carried within the log to move through the log and burn on the log""s surface.
Another advantage of the present invention is to provide a ceramic material which is sufficiently porous, containing microscopic and semi-microscopic pores to allow gas to pass through it, and which is well suited for use in making artificial versions of both active logs and passive objects such as non-burning logs and rocks.
A still further advantage of the present invention is to provide an artificial log which is cooled during operation by convection cooling resulting from gas fuel moving from an inner area to the outer surface of the log and absorbing heat energy, causing the log to cool and the gas to become warmer, thereby removing heat from the log and transferring it to the room or other area to be heated. The convection cooling provides a related advantage of providing a cooler and less hostile environment for the internal parts of the log apparatus, thus extending its useful life. The convention cooling also reduces thermally induced mechanical stress between the gas tube and ceramic portions of the active log, which expand at different rates with temperature.
Other objectives, advantages and novel features of the invention will become apparent to those skilled in the art upon examination of the specification and the accompanying drawings.